One issue confronting electrical power generating utilities is the rapid variability in demand during the day. Also, with the increasing use of alternate power sources by utilities such as wind and solar energy, there can be rapid variability in power generation. Power variances can prove problematic. For example, inability to meet peak demands and alternate source reductions can lead to “brown-outs” and/or “black-outs”. Another disadvantage faced by utilities involves paying a premium for electrical power purchased during peak load hours.
Peaking power plants must have a rapid response capability to match a rapidly changing demand and/or interruptions in supply. Although gas turbines have the ability to provide the rapid response required by peaking plants in about 1 to about 3 hours, they generally require a clean fuel. A clean gaseous fuel can be provided by the tail gases from a Fischer-Tropsch (FT) process.
In contrast to the method described in U.S. Pat. No. 5,543,437 (Benham et al) whereby the FT reactor synthesis gas flow rate, and hence production rate, was varied to accommodate a varying power demand, the instant method permits the FT reactor to operate at a constant synthesis gas flow rate.
U.S. Pat. No. 3,986,349 (Egan) teaches an integrated process for generating electrical power using gasification of solid carbonaceous material and FT technology. Gases from the gasifier and tail gases from the FT system are used in a power plant to produce base-load power. Liquid hydrocarbons from the FT system are stored and used as fuel in a gas turbine-generator set to provide supplemental power for peak-load demand.
Benham U.S. Pat. No. 5,543,437 contemplates the use of FT processes in combination with electric power generating facilities. When a fuel source for a steam power plant is obtained from coal or natural gas, the '437 patent suggests a variation in power production by changing the firing rate of the boilers. When the fuel source is from gas produced by a coal gasification facility, the '437 patent suggests adding an alternative use for the excess coal gas during off-peak hours. The alternate use can then be “turned down” when most of the gas is required for peak power production. An alternate use is a slurry-phase FT reactor for producing liquid hydrocarbons from the coal gas. Thus, the coal gasification facility supplies sufficient gas to meet peak electric load requirements while a minimum flow of gas is supplied to one or more FT reactors to produce liquid hydrocarbons during off-peak hours. In the change from peak-load operation to off-peak operation, coal gas is diverted from the boiler to the FT reactors and the pressure in the FT reactors is reduced to reduce the density of the coal gas and thereby increase the superficial velocity of the gas in the slurry FT reactor. During peak power production, the liquid hydrocarbon production rate of the slurry FT reactors drops.